Even if it had worked, the survivors would still be at risk of being killed by the infected. It'd just stop new infections.

The world wouldn't suddenly reverse, it wouldn't become safer. The small communities that are surviving would simply continue to do so as they are. The world would still be over. The infected would still be a huge threat.

It'd would only slightly improve survival rates. The people that get bitten and not torn to shreds would live, and that's it. Assuming further infections don't set in and take them out, or die from the injury itself.